The present invention relates to a movement control device for a vehicle, and in particular, relates to the movement control device for a vehicle which controls a movement of the vehicle equipped with front wheels steered.
Conventionally, a control device capable of controlling a movement of a vehicle so as to become stable when the vehicle's movement is unstable because of a slip or the like (such as an anti-sideslip apparatus) is known. Specifically, a control device, in which when it is detected that under-steering or over-steering movements happen to the vehicle during vehicle's cornering or the like, the speed of wheels are decelerated properly to restraint such movements, is known.
Meanwhile, another type of control device to adjust a load acting on the front wheels as the steered wheels (see US Patent Application Publication No. 2012/0209489 A1, for example) is known. This control device is different from the above-described control to improve the stable traveling of the vehicle when the vehicle movement is unstable, and adjusts deceleration during the cornering for adjusting the load acting on the front wheels so as to stabilize a series of driver's operations (braking, turning of steering, accelerating, returning of steering etc.) during the cornering of the vehicle traveling in a normal traveling state.
In the vehicle movement control device of the above-described patent document, for example, the traveling state of the vehicle during the cornering is detected and the deceleration control of the vehicle is performed by controlling an oil-pressure brake system based on its detection results. This oil-pressure brake system is generally configured to have some play among parts, so that there is a time lag between the input timing of control values to the oil-pressure brake system and the occurrence timing of the vehicle deceleration. Accordingly, it may be difficult for a conventional device to perform the deceleration control of the vehicle at an appropriate timing. Herein, the vehicle movement control device of the above-described patent document predicts a corner (curve) located in front of the traveling vehicle by using a camera and starts the control of the oil-pressure brake system before reaching the corner in order to solve the above-described difficulty, but this method may cause improper complexity of the device or costs increase.
The inventors of the present invention found through the investigations that the control for stabilizing the driver's operations during the cornering was possible by controlling a drive force of the vehicle, without using the brake system. Further, the inventors found that, it was possible in an electric-drive vehicle to adjust the deceleration by adjusting regenerative electric power, in particular, for the above-described stabilizing control, and this adjustment of the regenerative electric power enabled the direct drive-force adjustment through motor-torque decreasing (i.e., motor regeneration) properly, without generating the improper time lag caused by using the oil-pressure brake system.
Further, the inventors of the present invention found that it was effective to control the drive force of the vehicle based on a yaw-rate relating quantity relating to a yaw rate of the vehicle such that the drive force is decreased as the yaw-rate relating quantity increases, the rate of decreasing of the drive force being configured to become smaller according to an increase of the yaw-rate relating quantity. This is, the above-described control can cause a situation in which the vehicle has the deceleration quickly at the start timing of steering of the vehicle, thereby making the sufficient load quickly act on the front wheels as the steered wheels. Consequently, the friction between the front wheels as the steered wheels and a road surface increases and thereby the cornering force increases, so that the turning performance of the vehicle at an initial timing of the vehicle's cornering can be improved and thereby the responsiveness to the turning operation of the steering can be improved.
However, in a case in which the drive force of the vehicle is decreased when turn-back steering is conducted (when a driver operates a steering wheel to the right and the left repeatedly for a lane change, for example), the turning performance of the vehicle improves and thereby the yaw rate of the vehicle increases. Accordingly, in order to finish the turn-back steering, it may be necessary to return the steering wheel to its central position with a quick operation according to the increased yaw rate. However, if the driver's steering operation fails to follow the speed of the vehicle's yaw rate increasing, there is a concern that the yaw rate of the vehicle may not converge to zero (0) even at the timing when the vehicle turns ahead, so that the vehicle may continue its turning improperly.